The present invention relates to multifocal ophthalmic lenses. In particular, the invention provides progressive addition lenses designed for uses in which a large region of intermediate refractive power is desirable.
The use of ophthalmic lenses for the correction of ametropia is well known. For example, multifocal lenses, such as progressive addition lenses (xe2x80x9cPAL""sxe2x80x9d), are used for the treatment of presbyopia. The surface of a PAL provides far, intermediate, and near vision zones in a gradual, continuous progression of vertically increasing dioptric power from far to near focus, or top to bottom of the lens. PAL""s are appealing to the wearer because PAL""s are free of the visible ledges between the zones of differing dioptric power that are found in other multifocal lenses, such as bifocals and trifocals.
A number of activities require an especially large intermediate refractive power zone, which the typical PAL does not contain. For example, in viewing an image screen, such as a computer screen, an enlarged intermediate vision zone is desirable to avoid the need for the lens wearer to move the head from side to side to view the screen. Several customized, multifocal lens designs are known that provide an enlarged intermediate vision zone. However, these designs completely or partially sacrifice the far vision zone in order to provide the enlarged intermediate vision zone. Additionally, the intermediate vision zone of these designs is at least partially above the 0-180 degree axis of the lens causing the lens wearer to have to tilt the head forward in order to use this zone in visualizing an image screen.
Other designs, such as disclosed in U.S. Pat. No. 4,762,408, provide a wider intermediate vision zone, but only by increasing the channel length to 20 mm or more and by placing the near vision zone optical center at a point that does not permit the lens wearer""s pupil to access it without discomfort or head movement. Thus, a need exists for a PAL that overcomes some of the problems of these known designs.